The murder of the outspoken government critic on Wednesday prompted President Moncef Marzouki to cut short a foreign tour, one of his advisers, Ghassen Dridi, told Agence France-Presse (AFP). The presidency urged "restraint and wisdom".

Prime Minister Hamadi Jebali denounced the murder as an "act of terrorism" while the presidency in a statement dubbed it an "odious" crime designed to "lead the Tunisian people to violence".

Protests erupted in several Tunisian towns and demonstrators torched one Ennahda party office and ransacked another, as Belaid's brother accused the Islamist Ennahda party of being behind the assassination.

Jebali, from the Ennahda party, said a lone gunman wearing the traditional hooded, long burnous robe shot Belaid with three bullets fired at close range as he left his Tunis home on Wednesday morning.

"This is a criminal act; an act of terrorism not only against Belaid but against the whole of Tunisia," Jebali told private radio station Mosaïque FM, while promising to do everything possible to swiftly arrest the murderer.

"The Tunisian people are not used to such things. This is a serious turn ...
our duty to all, as a government, as a people, is to be wise and not fall into the criminal trap which seeks to push the country into chaos."

Belaid's wife told told Mosaïque FM her husband was hit by two bullets as he left home.

The murder of Belaid comes at a time when Tunisia is witnessing a rise in violence fed by political and social discontent two years after the mass uprising that toppled ex-dictator Zine El Abidine Ben Ali.

Several opposition parties and trade unions have accused pro-Islamist groups of orchestrating clashes or attacks against them.

Marzouki was in Strasbourg on Wednesday morning, where he took part in a session of the European Parliament and met Hollande. He was due to fly later to Cairo to attend a summit of the Organisation of Islamic Co-operation.

Belaid's party belonged to the Popular Front coalition of leftist parties that has emerged in opposition to the Tunisia government. – AFP